Eisige Zacken im Mondlicht auf Chajnantor
Babak Tafreshi, einer der ESO-Fotobotschafter, hat ein ausgefallenes Phänomen auf dem Chajnantor-Plateau aufgenommen, dem Standort für das Atacama Large Millimeter/submillimeter Array (ALMA).
Diese bizarren Eis- und Schneeformationen nennt man auch Büßereis (spanisch penitentes). Sie werden durch das Licht des Mondes beleuchtet, der rechts im Bild zu sehen ist. Auf der linken Seite und höher am Himmel können die Kleine und Große Magellansche Wolke gerade eben noch erkannt werden, während weiter links nahe am Horizont das rötliche Leuchten des Carinanebels auftaucht.
Die Zacken sind natürliche Wunderwerke in großen Höhen, so wie hier in den Chilenischen Anden, wo man sie typischerweise in Höhen ab 4000 Meter über dem Meeresspiegel findet. Es handelt sich um spitze Nadeln und Plättchen aus verhärtetem Schnee, die sich oft in Haufen ansammeln und mit den flächigen Seiten zur Sonne zeigen. Sie erreichen Höhen von einigen Zentimetern (nicht unähnlich Grasflächen) – bis hin zu 5 Metern – und erzeugen damit den Eindruck eines verschneiten Waldes mitten in der Wüste.
Die genauen Details zur Formbildung der Nadeln sind teilweise immer noch unverstanden. Für viele Jahre glaubten die Menschen der Anden, dass das Büßereis das Resultat der häufigen starken Winde in den Bergketten der Anden sind. Allerdings geht man heute davon aus, dass sie ein Produkt einer Kombination von verschiedenen physikalischen Phänomenen sind.
Der Entstehugnsprozess beginnt mit Sonnenlicht, das auf die Oberfläche des Schnees fällt. Wegen der Trockenheit in der Wüste sublimiert das Eis und schmilzt nicht – es geht vom festen Zustand ohne zu schmelzen und damit den flüssigen Zustand direkt in die gasförmige Phase über. Oberflächenmulden im Schnee reflektieren Licht und führen zu erhöhter Sublimation und tieferen Senken. Innerhalb der Senken sorgen erhöhte Temperatur und Feuchtigkeit für das Aufschmelzen. Diese positive Rückkopplung beschleunigt das Wachstum der charakteristischen Strukturen des Büßereises.
Die eisigen Kreaturen sind nach den stacheligen Kopfbedeckungen der Nazarenos benannt, Mitgliedern einer Bruderschaft, die an Osterprozessionen rund um die Welt teilnahmen. Es fällt nicht schwer sie als eisige Gruppe von Mönchen zu erkennen, die sich im Mondlicht versammeln.
Das Bild wurde am Rand der Straße zu ALMA aufgenommen. Das Observatorium, dass seine wissenschaftlichen Beobachtungen am 30 September 2011 begonnen hat, wird letztendlich aus 66 Präzisionsantennen bestehen, die wie ein einzelnes, großes Teleskop zusammenarbeiten.
Links
Herkunftsnachweis:ESO/B. Tafreshi (twanight.org)
Über das Bild
| ID: | potw1221a |
| Sprache: | de |
| Typ: | Fotografisch |
| Veröffentlichungsdatum: | 21. Mai 2012 10:00 |
| Größe: | 4200 x 3012 px |
Über das Objekt
| Name: | Atacama Desert |
| Typ: | Solar System : Planet : Feature : Surface |
Mounted Image
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